III group nitrides, such as gallium nitride, draw more and more attentions because they can be widely used in light-emitting diodes (LEDs) of semiconductor lighting devices as well as high-power electronic devices. Due to lack of intrinsic substrates, gallium nitride devices are generally prepared on heterogeneous substrates, such as sapphire, silicon carbide and silicon. Due to their wide applications, silicon substrates have the best size and quality among the above-mentioned substrate materials. Currently, complementary metal oxide semiconductors (CMOSs) are mainly manufactured based on 12-inch silicon substrates. In addition, silicon has the best economy among the above-mentioned substrate materials. Therefore, the best way to reduce costs of gallium nitride based devices is to prepare gallium nitride materials on large-sized silicon substrates.
However, because there are huge lattice mismatch and thermal mismatch between gallium nitride and silicon, a lot of stresses will be introduced during the processes of preparation and cooling. Such stresses will result in warping of epitaxial layers and cracking of epitaxial films, and bring damages to the silicon substrates themselves. Due to residual stresses in the silicon substrates, gallium nitride epitaxial layers on the silicon wafers may be broken during the manufacturing processes, thereby bringing huge losses. To avoid this, a usual approach is to use thick silicon substrates. However, there is a limit for thicknesses of the substrates due to processing conditions. If a thickness of a silicon substrate exceeds a certain threshold, the substrate cannot be treated by processing apparatus, for example, it cannot be focused and aligned by a lithography apparatus, thus the processing cannot be implemented.
Therefore, in view of the above-mentioned technical problems and improvement methods, it is necessary to provide a semiconductor substrate, a semiconductor device and a manufacturing method of the semiconductor substrate.